Relapsing fever is a group of infections caused by spirochetes in the genus Borrelia that are characterized by recurrent fever and found throughout the world (1, ...MicrobesHomeEditorialBoardReviewsContactUsSearchBorrelia species(RelapsingFever)Authors:PeterJ.Krause,M.D.Authors,SecondEdition: TeshaleSeboxa,MD,M.SC(CTM);DanielFekade,M.D.MonographTablesWhat'sNewReviewsHistoryMICROBIOLOGYRelapsingfeverisagroupofinfectionscausedbyspirochetesinthegenus Borrelia thatarecharacterizedbyrecurrentfeverandfoundthroughouttheworld(1, 15, 16, 19, 24, 27, 31, 32, 33, 38, 42, 47, 52,56, 59, 61, 69, 70, 71, 76, 78, 82, 86).These Borrelia aretransmittedeitherbylice(louse-bornerelapsingfeverorLBRF),soft-bodiedticks(softtick-bornerelapsingfeverorSTBRF),orhardbodiedticks(hardtick-bornerelapsingfeverorHTBRF).Distinctfebrileepisodesareaccompaniedbynon-specificsymptomsseparatedbyperiodsofverymildsymptomsorwellness(1, 15, 16, 19, 24, 27, 31, 32, 33, 38, 42, 47,52, 56, 59, 61, 69, 70, 71, 76, 78, 82, 86).Relapseoffeverandassociatedsymptomsarecausedbycyclesofrisingspirochetemiaandanassociatedimmuneresponsecharacterizedbydiminutioninthenumberofspirochetes,immuneevasionbyasubsetofspirochetes,andaresurgenceinspirochetemia.Relapsing feverborreliaarespirochetalbacteriawhosespiralshapeenhancestheirmotility(Figure1).Theycontainalinearchromosomeandseverallinearandcircularplasmids.Innerandoutercellmembranesareseparatedbyaperiplasmicspacethatcontainsabundleofflagella,which arenotsurfaceexposed(8, 36, 49, 91).Flagella emergefromeachendoftheorganismandoverlapinthemiddle.They areresponsibleforshapeandmotility.Themostabundantsurfacelipoproteinsoftheoutermembranearevariablemajorproteins(Vmps)thatdetermineserotypeidentity(4, 5, 68).  Achangeintheexpressionofvariablemajorproteinsenablesrelapsingfeverborreliatosurviveinvertebratehostsandduringtransmissionbetweenavertebratehostandarthropodvector(5, 68, 77). Alterationinvariablemajorproteinsallowescapefromadaptiveimmuneattackandsustainedspirochetemiainmammalianr